CC and CS descriptions of phase-sensitive cross sections: computations for He+HCl

Detailed CC (coupled-cluster) and CS (coupled states or centrifugal sudden) calculation, for the He + HC1 system, of a wide variety of cross sections which are sensitive to the phase of the differential scattering amplitude are reported. The CS approximation gives a valid description of the scattering at a remarkably detailed level, although accuracy is not uniform for the various types of cross sections. Exact CC results show a strong propensity for j /su z/ preservation along the geometric or kineamatic apse. These results strongly indicate that the CS approximation provides a basically correct physical description of the He + HC1 collision system, and that its accuracy for detailed cross sections is not just the result of fortuitous cancelation of errors